Type 1 diabetes mellitus (DM) is usually precipitated by autoimmune destruction of pancreatic β-cells, leading to insufficient insulin production (Reference 1). Since clinical symptoms are caused by diminished production of a single protein, diabetes is a natural candidate for treatment by gene therapy. The basic components of insulin gene therapy are widely available. Functional insulin genes can be transferred to multiple tissues (References 2-4), and the capacity of non-β-cells to secrete biologically active transgenic insulin in sufficient quantities to affect metabolism is well established (References 2-6). Multiple investigators have demonstrated functional insulin gene transfer both in vitro, and in vivo (References 2 and 7-8). However, attempts to regulate transgenic insulin production have proven inadequate (References 9-10). Consequently, in a variety of insulin gene transfer protocols secretion of transgenic insulin has been either insufficient to normalize blood glucose (References 2-5 and 10), has affected glycemia only moderately, or for short periods of time (References 4, 5 and 10-14), or has produced lethal hypoglycemia (References 2-3 and 8). Thus, for insulin gene therapy to be effective, it is widely accepted that insulin production must be regulated.
The critical importance of regulated transgenic insulin production was underscored by the work of Muzzin, et al. They successfully induced insulin production from the livers of STZ-treated rats by administering a retrovirus containing an insulin transgene (Reference 3). Transgenic insulin secretion was sufficient to prevent diabetic ketoacidosis, while permitting the animals to gain weight. Moreover, they avoided lethal hypoglycemia in a subset of animals by limiting vector dosage. However, reductions in vector sufficient to enable survival with prolonged fasting produced hyperglycemia when the animals were fed, presumably because transgenic insulin production could not increase to meet expanded demand (Reference 3). Others have demonstrated transgenic insulin secretion that is regulated by cAMP, glucocorticoids, insulin, or glucose by utilizing metabolically sensitive promoters in hepatocytes or hepatoma cells, and Simpson et al have demonstrated glucose responsiveness in insulin expressing HepG2 cells (References 15-18). However, transfer of these regulatory mechanisms to in vivo models has been difficult (Reference 9). We have overcome these limitations, and have developed a glucose and insulin sensitive promoter capable of appropriately coupling metabolic requirements for insulin, with insulin production from the liver of a diabetic animal.